1. Field of the Invention
The invention generally relates to guided projectiles, and more particularly to a fin-stabilized guided projectile.
2. Description of the Related Art
Generally, artillery projectiles launched from cannons require mechanical and aerodynamic stabilization to assure a predictable trajectory. Until recently, most artillery projectiles were generally stabilized by means of angular momentum (spinning inertia). This technique commonly referred to as spin stabilization, is achieved by spinning the projectile about its longitudinal axis as it translates along the bore of the cannon. FIG. 1 shows an example of the general configuration of a conventional spin stabilized projectile consisting of an ogive 1 adjacent to a forward bore rider 2, which is next to a shell body 3 that is adjacent to an obturating (gas-sealing) rotating band 4, which is adjacent to a tailboom 5 all formed and spinning about the longitudinal axis of the spin stabilized projectile during flight. This rotation (spin) motion is achieved by mechanical contact between the helical rifling grooves and lands engraved on the surface of the cannon bore mating with a deformable metallic or polymeric ring of material, referred to as the rotating band 4 mounted on the rear of the projectile.
In practice, this motion causes the projectile to spin about the longitudinal axis of the projectile thereby acquiring some magnitude of angular momentum that is conserved (retained) as the projectile exits the muzzle. One disadvantage associated with the spin stabilization method is the potential for excessive angular acceleration imparted to the entire projectile. The associated axial and centrifugal loads may result in prohibitively high inertial forces acting on projectile components.
Additionally, the potential to over-stabilize the projectile, which may prevent tip-over at the point of apogee, exists with spin-stabilized projectiles. In these cases, the projectile may approach or impact the target at an orientation other than nose (ogive 1) first thereby resulting in a malfunction and a failed or delayed detonation. Another characteristic of over-stabilized projectiles is their tendency to drift off their intended trajectories resulting in excessive dispersion and/or unintended collateral damage.
Artillery projectile designers have applied the fin stabilization technique in an effort to diminish or eliminate some of the disadvantages associated with spin-stabilized projectiles. Fin-stabilized projectiles have the advantage of operating in a uniaxial acceleration loading environment (as opposed to the dual acceleration environment, axial and angular, of the spin-stabilized projectiles). FIG. 2 shows a conventional fin-stabilized projectile with the fins 6 configured as they would be during flight.
Fin stabilization has proven successful in the past and is considered an enhancement to both direct fire and indirect fire munitions. One of the major advantages to this technique is that a single smoothbore cannon can be used conventionally for high velocity direct fire fin stabilized kinetic energy penetrators (mounted in sabots) in addition to launching the relatively lower velocity full bore indirect fire artillery projectiles.
A disadvantage of the fin stabilization method is that the fins must be capable of assuming a stowed configuration for translation through the bore of the cannon during launch, and a deployed configuration for aerodynamic stability during flight. Conventional full-bore fin stabilized artillery projectiles usually employ some form of a complex mechanism requiring on-board energy sources or powered mechanisms such as electric batteries, motors, solenoids, squibs (explosives) or spring-loaded (pre-compressed) mechanical devices. Some potential complications associated with these devices include a possible requirement that they integrate precise timing mechanisms or electrical circuits to activate and deploy the fins within a short distance after the projectile exits the muzzle of the cannon. Therefore, there remains a need for a novel full-bore artillery projectile fin deployment mechanism which is not dependent on the use of any electromechanical or complicated stored potential energy actuation devices.